Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
BONTRIL vs ACTIDIL
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Bontril (phendimetrazine) is a sympathomimetic amine that acts as an appetite suppressant. Its mechanism involves stimulating the hypothalamus to release norepinephrine and dopamine, which reduces hunger cues. It is a prodrug that is metabolized to the active agent phenmetrazine, which inhibits reuptake and increases release of norepinephrine and dopamine in the central nervous system.
H1-receptor antagonist; competes with histamine for H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract, blocking histamine-induced bronchoconstriction, vasodilation, and increased capillary permeability.
FDA-approved for management of obesity as a short-term adjunct (few weeks) in a regimen of weight reduction based on caloric restriction, exercise, and behavior modification. Off-label uses are not well documented due to limited evidence.
Allergic rhinitis,Allergic conjunctivitis,Urticaria,Angioedema
BONTRIL 50 mg orally once daily, with or without food.
2.5 mg orally every 4 to 6 hours as needed; maximum 10 mg per day.
18-24 hours; prolonged in renal impairment (up to 40 hours) requiring dose adjustment.
Terminal elimination half-life is approximately 20-25 hours in healthy adults; may be prolonged in elderly or patients with hepatic impairment.
Phendimetrazine is extensively metabolized in the liver, primarily via N-demethylation to its active metabolite phenmetrazine. Minor pathways include hydroxylation and conjugation. Cytochrome P450 enzymes are involved, though specific isoforms are not fully characterized.
Hepatic via CYP450 isoenzymes (primarily CYP3A4 and CYP2D6); undergoes N-demethylation and N-oxidation.
Primarily renal (60-70% unchanged) with minor biliary/fecal (10-15% as metabolites).
Renal excretion of unchanged drug and metabolites accounts for approximately 60-80% of the administered dose; biliary/fecal elimination comprises the remainder (20-40%).
85-90% bound to albumin and alpha-1-acid glycoprotein.
Approximately 90% bound to plasma proteins, primarily albumin.
3-5 L/kg; indicates extensive tissue distribution.
2.5-4.0 L/kg, indicating extensive tissue distribution.
Oral: 70-80% (first-pass metabolism); IV: 100%.
Oral bioavailability is approximately 50-60% due to first-pass metabolism.
GFR >60 m L/min: no adjustment. GFR 30-60 m L/min: reduce dose to 25 mg once daily. GFR <30 m L/min: use is not recommended.
GFR 10-50 m L/min: 2.5 mg every 6-8 hours; GFR <10 m L/min: 2.5 mg every 8-12 hours.
Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose to 25 mg once daily. Child-Pugh Class C: use is contraindicated.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: contraindicated.
Weight-based: 1 mg/kg orally once daily, with a maximum of 50 mg. Not recommended for children weighing less than 10 kg.
Children 2-5 years: 1.25 mg orally every 4-6 hours (max 5 mg/day); Children 6-12 years: 1.25-2.5 mg every 4-6 hours (max 7.5 mg/day).
Start at 25 mg orally once daily; may increase to 50 mg after 2 weeks if tolerated and renal function is adequate (Cr Cl >60 m L/min).
Initiate at 1.25 mg orally every 6-8 hours; maximum 5 mg per day due to increased risk of anticholinergic effects and renal impairment.
None
None
Risk of abuse, dependence, and tolerance; monitor for signs of addiction.,May cause serious cardiovascular events including pulmonary hypertension and valvular heart disease, especially with long-term use.,May impair ability to drive or operate machinery due to dizziness or blurred vision.,Use with caution in patients with hypertension, hyperthyroidism, glaucoma, or history of drug abuse.,Concomitant use with other sympathomimetics or MAO inhibitors can cause hypertensive crisis.,Not recommended for use in patients with a history of epilepsy or those taking other anorectic agents.
May cause drowsiness and impair mental alertness,Avoid alcohol and other CNS depressants,Use with caution in patients with narrow-angle glaucoma, prostatic hypertrophy, or urinary retention,Elderly patients are more susceptible to anticholinergic effects
Known hypersensitivity to phendimetrazine or any component of the formulation.,History of cardiovascular disease including coronary artery disease, arrhythmias, or congestive heart failure.,Hypertension (moderate to severe).,Hyperthyroidism.,Glaucoma.,History of drug abuse or alcoholism.,Concurrent use of monoamine oxidase inhibitors or within 14 days of such use.,Pregnancy and breastfeeding.,Agitated states.,History of seizure disorders.
Hypersensitivity to any component,Concurrent use with monoamine oxidase inhibitors
Avoid high-fat meals as they may delay absorption of oral formulations. No specific food-drug interactions known; however, anticholinergic effects may be exacerbated by alcohol.
No specific food interactions, but taking with food may reduce GI side effects. Alcohol should be strictly avoided due to additive CNS depression. Grapefruit juice is not documented to interact.
BONTRIL is classified as FDA Pregnancy Category X. First trimester: high risk of major congenital malformations including neural tube defects, cardiovascular anomalies, and cleft palate. Second and third trimesters: risk of fetal growth restriction, oligohydramnios, and neonatal respiratory depression if used near term.
First trimester: Limited human data; animal studies show no teratogenicity. Second and third trimesters: Not associated with major congenital malformations. However, anticholinergic effects may cause neonatal tachycardia, irritability, and withdrawal symptoms if used near term.
No data available on excretion into human breast milk. M/P ratio unknown. Due to potential for serious adverse effects in nursing infants, breastfeeding is contraindicated during BONTRIL therapy.
Excretion into breast milk likely but negligible amounts; no adverse effects reported in infants. M/P ratio not established. Considered compatible with breastfeeding; monitor for sedation or irritability in neonate.
No dose adjustment required for pregnancy. However, due to teratogenicity, BONTRIL should be discontinued before conception or as soon as pregnancy is diagnosed.
No specific dose adjustments required in pregnancy; however, use lowest effective dose due to potential anticholinergic effects. Pharmacokinetics may be altered (increased volume of distribution), but no dose adjustment recommended.
BONTRIL (hyoscyamine) is an anticholinergic used for GI spasms; avoid in patients with glaucoma, myasthenia gravis, or obstructive uropathy. Onset of action is 2-3 minutes IV; monitor for heat stroke in high ambient temperatures due to decreased sweating.
ACTIDIL (triprolidine) is a first-generation antihistamine with sedative properties. Use cautiously in elderly due to risk of confusion, urinary retention, and falls. Avoid in patients with narrow-angle glaucoma, BPH, or asthma. Administer with food if GI upset occurs. Onset of action is 30-60 minutes; duration 4-6 hours.
Do not drive or operate machinery until you know how this medication affects you, as it may cause dizziness or blurred vision.,Avoid alcohol and other CNS depressants as they may increase sedation.,Report immediately if you experience eye pain, difficulty urinating, or rapid heartbeat.,Use caution in hot weather; this drug reduces sweating and increases risk of heat stroke.
Do not drive or operate heavy machinery until you know how this medication affects you; it can cause drowsiness.,Avoid alcohol and other CNS depressants, as they may increase sedation.,Take exactly as prescribed; do not exceed recommended dose.,If you miss a dose, skip it; do not double the next dose.,Notify your doctor if you experience blurred vision, difficulty urinating, or severe drowsiness.,Do not use for prolonged periods without medical advice.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about BONTRIL vs ACTIDIL, answered by our medical review team.
BONTRIL is a Sympathomimetic Anorectic that works by Bontril (phendimetrazine) is a sympathomimetic amine that acts as an appetite suppressant. Its mechanism involves stimulating the hypothalamus to release norepinephrine and dopamine, which reduces hunger cues. It is a prodrug that is metabolized to the active agent phenmetrazine, which inhibits reuptake and increases release of norepinephrine and dopamine in the central nervous system.. ACTIDIL is a Antihistamine that works by H1-receptor antagonist; competes with histamine for H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract, blocking histamine-induced bronchoconstriction, vasodilation, and increased capillary permeability.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between BONTRIL and ACTIDIL depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of BONTRIL is: BONTRIL 50 mg orally once daily, with or without food.. The standard adult dose of ACTIDIL is: 2.5 mg orally every 4 to 6 hours as needed; maximum 10 mg per day.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between BONTRIL and ACTIDIL in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. BONTRIL is classified as Category C. BONTRIL is classified as FDA Pregnancy Category X. First trimester: high risk of major congenital malformations including neural tube defects, cardiovascular anomalies, and cleft p. ACTIDIL is classified as Category C. First trimester: Limited human data; animal studies show no teratogenicity. Second and third trimesters: Not associated with major congenital malformations. However, anticholinergi. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.